1. Field of the Invention
The present invention relates to a tee nut, and more particularly, it relates to a tee nut comprising a hollow shaft portion which is provided with a female screw on its inner peripheral surface, and a flange portion, outwardly extending from an end of the shaft portion, provided with a plurality of pawls.
2. Description of the Background Art
FIG. 9 is a perspective view showing a conventional tee nut 1, which is of interest to the present invention.
The tee nut 1 comprises a shaft portion 2 and a flange portion 3 outwardly extending from a first end of the shaft portion 2, which are integrally made of a metal material. The shaft portion 2 is in the form of a hollow cylinder, which is provided with a female screw 4 on its inner peripheral surface. The female screw 4 is formed along the overall inner peripheral surface of the shaft portion 2.
On the other hand, the flange portion 3 is provided with two pairs of pawls 5, 6, 7 and 8, which are opposite to each other along a radial direction of the flange portion 3, extending from the first end toward a second end of the shaft portion 2. These pawls 5 to 8 are formed by upwardly bending parts of the outer peripheral edge of the flange portion 3.
Such a tee nut 1 is fixed to an object such as a timber, for example, by inserting the shaft portion 2 in a hole which is previously provided in the object and driving the pawls 5 to 8 into the object. Upon such fixing to the object, the tee nut 1 is inhibited from rotation so that a screw member such as a bolt can be fitted into and engage with the female screw 4 which is formed on the inner peripheral surface of the shaft portion 2.
Such a tee nut 1 is generally called a "hopper feed tee nut", since the tee nut 1 can be smoothly moved along a feed track which is provided on a nut fixer device used for fixing the same to the object, for enabling automatic feeding of successive tee nuts. For example, British Patent No. 1,157,734 describes a type of such a hopper feed tee nut in detail.
FIG. 9 shows the aforementioned feed track 9 in phantom dashed lines. This feed track 9 comprises a pair of guide rails 10 and 11 having C-shaped sections, which are symmetrically arranged to be opposite to each other. The flange portion 3 is slidingly received in these guide rails 10 and 1, so that the tee nut 1 is moved along the feed track 9 in a prescribed orientation while locating the pawls 5 to 8 between the guide rails 10 and 11. The feed track 9 is frequently bent to bring the tee nut 1 into a desired position or orientation although such a bent state is not shown in FIG. 9, so that the shaft portion 2 is aligned with a hole which is provided in the object in which the tee nut is to be installed (not shown).
However, the aforementioned fixing of the tee nut 1 to the object is maintained substantially only by the pawls 5 to 8 biting into the object. The pawls 5 to 8 thus biting into the object may become so loosened over time that the tee nut 1 becomes unfixed or falls out of the object in the worst case. FIGS. 10 and 11 show another conventional tee nut 12, which has been proposed in order to solve such a problem. FIGS. 10 and 11 are a front elevational view and a bottom plan view showing the tee nut 12 respectively.
This tee nut 12 comprises a shaft portion 13 and a flange portion 14 outwardly extending from a first end of the shaft portion 13, which are integrally made of a metal material, similarly to the aforementioned tee nut 1. The shaft portion 13 is in the form of a hollow cylinder and has a flarable or splayable portion 15 in a second end which is opposite to the aforementioned first end, while a female screw 16 is formed on an inner peripheral surface portion excluding the flarable or splayable portion 15. The flarable or splayable portion 15 has a relatively small thickness to facilitate later flaring or splaying the portion 15 as described below.
On the other hand, the flange portion 14 is provided with two pairs of pawls 17, 18, 19 and 20, which are opposite to each other along a radial direction of the flange portion 14, and extend from the first end toward the second end of the shaft portion 13. These pawls 17 to 20 are formed by upwardly bending parts of the outer peripheral edge of the flange portion 14.
Such a tee nut 12 is used in the manner shown in FIG. 12, for example. Referring to FIG. 12, an object 21 such as a timber, for example, is previously provided with a through hole 22. The shaft portion 13 of the tee nut 12 is inserted in this through hole 22. In this state, the flarable or splayable portion 15 shown in FIG. 10 is splayed or flared by a flaring tool, so that a splayed or flared rim 15a is formed on one surface of the object 21. At the same time, the pawls 17 to 20 are driven into the other surface of the object 21. Thus, the tee nut 12 is completely fixed to the object 21.
In such a mounting state of the tee nut 12, the pawls 17 to 20 inhibit the tee nut 12 from rotation with respect to the object 21, while the flange portion 14 and the splayed or flared rim 15a hold the object 21 in an axial direction to inhibit disengagement of the tee nut 12 from the through hole 22. Thus, the tee nut 12 is strongly fixed to the object 21, and such a fixed state is semipermanently maintained.
This tee nut 12 is also applied as a "hopper feed tee nut", similarly to the aforementioned tee nut 1. Therefore, the tee nut 12 is also moved along the feed track 9 shown in FIG. 9. When a plurality of such tee nuts 12 are moved along the feed track 9, however, the movement is frequently hindered in a manner described as follows.
The flange portion 14 of the tee nut 12 is substantially in the form of a circle before formation of the pawls 17 to 20. Therefore, the pair of pawls 17 and 18 and the other pair of pawls 19 and 20 are coupled with each other by arcuate sides 23 and 24 respectively. When a plurality of tee nuts 12 are serially moved along the feed track 9 (see FIG. 9), therefore, the flange portions 14 tend to overlap with those of adjacent tee nuts 12. Consequently, the tee nuts 12 are frequently erroneously fed along the feed track 9 or therein.
On the other hand, the flange portion 3 of the tee nut 1 shown in FIG. 9 is in the form of an octagon as a whole, and the paired ones of the two pairs of pawls 5, 6, 7 and 8 are coupled with each other by linear sides 25 and 26 respectively. The linear side edges of flange portion 3 hold the tee nut in a prescribed orientation and prevent overlapping of adjacent tee nuts in feed track 9. When a plurality of such tee nuts 1 are fed along the feed track 9, therefore, the flange portions 3 relatively rarely cause the aforementioned overlapping phenomenon.
Thus, it is expected that it is possible to reduce the aforementioned overlapping phenomenon in the tee nut 12 shown in FIGS. 10 and 11 by changing the shapes of the arcuate sides 23 and 24 of the flange portion 14 to be linear side edges. However, the arcuate shapes cannot be so easily changed as hereinafter described, and in practice, it is impossible to find such a modified tee nut in the market.
In general, the tee nut 12 is obtained by drawing a strip-shaped metal plate. Such a strip-shaped metal plate is fed along a progressive die to be worked in a prescribed order, so that an intermediate product is separated from the strip-shaped metal plate in a stage subjected to working for obtaining some of the features of the tee nut 12. This intermediate product has portions corresponding to the shaft portion 13 and the substantially circular flange portion 14, with slits for forming the pawls 17 to 20. The intermediate product is then grasped by a tool chuck on the portion corresponding to the flange portion 14, so that the flarable or splayable portion 15 and the female screw 16 are formed in the portion corresponding to the shaft portion 13 in this state. The flarable or splayable portion 15 is formed by cutting the inner peripheral surface of the shaft portion 13 with a cutting tool for reducing the wall thickness. Thereafter the pawls 17 to 20 are bent or raised up from the flange portion 14, to obtain the desired tee nut 12.
The flange portion 14 is substantially in the form of a circle before formation of the pawls 17 to 20 as hereinabove described, in relation to the grasping of the intermediate product by a chuck for forming the flarable or splayable portion 15. If the flange portion 14 to be grasped by the chuck has a substantially circular shape, it is possible to grasp the flange portion 14 in the chuck while properly centering the shaft portion 13 for the machining operation since the flange portion 14 has no directivity with respect to such chucking. In this case, further, the flange portion 14 has no corner on in its outer peripheral portion, whereby no flash is caused by the chuck grasping the flange portion 14 since no outer peripheral part of the flange portion 14 is crushed by the chuck.
On the other hand, it is difficult to grasp in a chuck the flange portion 3 having a substantially octagonal shape as shown in FIG. 9, due to its directivity, while it is also difficult to center the shaft portion 2. When the flange portion 3 is grasped in a chuck, further, corners of the flange portion 3 may be compressively deformed to result in flashes. Such flashes inhibit the tee nut 1 from moving smoothly along the feed track 9. While a chuck having a specific structure may be employed in order to solve the aforementioned problem, it is necessary to regularly set the flange portion 3 along a constant direction with a specific orientation, through a complicated operation when using such a chuck.
In the tee nut 12 having the flarable or splayable portion 15 as shown in FIGS. 10 and 11, therefore, the flange portion 14 must be substantially in the form of a circle in a stage before formation of the pawls 17 to 20.